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81 comments on The Energy Return on Time

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Nate Hagens on July 25, 2007 - 11:51am Permalink | Subthread | Parent | Comments top

robert-funny you should mention that. Water too, may be a limiting variable as Peak Oil unfolds. Two colleagues and I have a paper pending in Science called "Burning Water - The Energy Return on Water Invested", showing that many alternative energy technologies, especially biofuels, use an order of magnitude more water than fossil fuel extraction. Wind and solar obviously use next to none. We calculated "EROWI" statistics for 8 different energy sources. We also showed that in the next 20 years, a majority of the world population will live in countries that have zero or minimal extra water to allocate to energy production -I will post a summary of that paper here once/if it gets published.

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robert2734 on July 25, 2007 - 12:35pm Permalink | Subthread | Parent | Comments top

http://www.pennwellblogs.com/sst/eds_threads/labels/HSMC.php

Silicon fabs use a lot of deionized water but I don't have a number it is probably recycleable. Compared to thermoelectric or ethanol, it is probably close enough to none.

Given cheap energy, making clean water is trivial. But clean water is necessary to make energy.

Ireland exported food during the potato famine. As did India during some terrible 19th century famines when the monsoons failed. Food and energy will follow the money this upcoming century. Before railroads, it was impossible to move staple foods by land in or out of a famine area. Maybe that was a good thing.

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Spaceman on July 25, 2007 - 9:53pm Permalink | Subthread | Parent | Comments top

Hi Nate,
Thanks for your work.
See if you can get in touch with this guy http://www.sredmond.com/vthr_index.htm
He has a modified wood gasifier that he claims works best with green wood chips.

In the experimental furnace I'm studying, combustion is aided by being slowed down. Damp fuel means that the air supply can be filtered through the chips to adequately supply the needs of the slow burning upper hot layer. Faster combustion would yield insufficient air supply for the upper layer and a fuel-rich condition.

What this means is, in the VTHR furnace, if we use dry fuel, we get smoke. If we use green wood it burns cleanly. This is just one of the many non-intuitive aspects of this design.

(I commented on this at your previous post but days after it was posted).

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Nate Hagens on July 25, 2007 - 10:31pm Permalink | Subthread | Parent | Comments top

Hmmm.
This sounds very curious to me. Im not really a firewood expert per se other than doing some numbers - everyone has been pretty emphatic in telling me that wet wood is a no-no, which is why they work so hard to dry it - many even put some extra wood they are about to burn NEXT to the woodstove for a day or two while its on, so as to get extra dry. I'll check out the link, but my mind is already working on why we WANT so much stuff and the drivers that underlie this behaviour....

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expat on July 26, 2007 - 12:52am Permalink | Subthread | Parent | Comments top

There might be a two other reasons for that - the wood helps as thermal mass to keep the area warmer longer, and a wood stove is very dry, and to the extent more water is in the air, the more comfortable it is. (Yes, the amount is truly trivial - but sometimes, we don't notice benefits/disadvantages when looking at what we do.) I specifically try to dry wet clothes when the fire is burning, for just that reason - though the main reason, of course, is that they dry faster.

But the other thing about storing/drying firewood - how cold is it when you bring it in? I try to stack a few days worth of wood in the sun, and bring it in near the stove in the afternoon - wood in the room at 55° F is a lot better than wood at 25° F. The unheated basement is my other burning storage area, a solution for a week of gray and damp days around freezing.

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NZSanctuary on July 26, 2007 - 12:30am Permalink | Subthread | Parent | Comments top

Hi Nate, great article. The first part would make an excellent primer too.

Would be very interested to see what the EROWI paper says.

Cheers :)

"You can never solve a problem on the level on which it was created."
Albert Einstein

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